Fountain solution for planographic printing



United States This invention relates to improvements in aqueous fountain fluids which are employed in the process of planographic printing.

Planographic printing involves the preparation of a master plate having Water-receptive non-print portions and water-repellent ink-receptive portions, constituting an image to be produced. The plate is moistened with an aqueous fountain fluid, repelled by the image, to render and maintain the'non-print portions of the plate ink-repellent, and is then inked with printing ink to deposit the same on the ink-receptive image portions. The

-ink is then transferred from the image, usually by an offset blanket to a copy sheet, to form an impression of the image thereon. The moistening, inking and transfer operations are successively repeated for the production of large numbers of copies.

Plates to be employed in planographic printing are provided with a surface which is adapted to constitute the non-print background, and likewise adapted to receive and retain an ink-receptive water-repellent image. The latter is formed by inscribing the plate with an oleophilic image-forming composition, or by photographic processes, for example, by sensitizing the plate with a light-sensitive gelatin-bichromate coating or a light-sensitive diazo compound if desired in admixture with a resin which, upon exposure to light through a master is insolubilized and rendered ink-receptive, whereupon the unexposed portions are washed away, e.g. with water or an organic solvent exposing the underlying plate surface constituting the non-print background. Such plates can also be obtained by the electrophotographic process. The plates can be made of a metal, such as Zinc or aluminum of which the surface is modified as by etching or graining to render them Waterreceptive; or of materials such as vegetable parchment, which possess the desired hydrophilic as well as imageretaining properties; or the surface may be made of a hydrophilic insoluble colloid coating, such as casein formaldehyde, insolubilized polyvinyl alcohol, or insolubilized carboxymethyl cellulose compounds.

In using the aforesaid plates for planographic printing, an aqueous solution, often referred to as an etch, is is initially applied to the plate, the solution containing ingredients adapted to moisten the non-print background portions of the plate and render them ink-repellent. A similar solution is employed in the fountain of the printing press for moistening the plate before each inking operation, the solution being compounded to maintain the non-print background of the plate ink-repellent and to prevent spreading of the image, While at the same time avoiding undermining of the image. The useful life of the plate for printing copies is largely dependent upon the maintenance by the action of the fountain fluid of a balance between the ink-receptive image portions and water-receptive non-print background portions so as to prevent encroachment of either upon the other. Solutions heretofore employed for moistening the plates, both as etch and as fountain solutions, ordinarily included a colloid thickener such as gum arabic, gum tragacanth, or the like to impart desired properties, such as adherence to the. plate without undermining the image.

- elude therein a preservative, such as phenol or a pheno ice PatentedApr. 1Q, 1962 to the image.

The colloidal thickeners commonly-employed in such solutions, e.g. gum arabic, gum tragacanth, soluble starch and the like constitute excellent media in the aqueous mixtures in which they are employed, for the growth of molds, bacteriaand the like, which alter the properties of the solutions and render them useless for the intended purposes. The use of carboxymethyl cellulose instead ofnatural thickeners improves the stability of such solutions against such bacteria. Thus, if solutions which have soured or spoiled are applied to a printingplate, they can ruin the plate for further use, causing serious losses in time, effort and expense. While the solutions can be manufactured and distributed in sealed containers under sterile conditions, they are subject to contamination as soon as they are opened and eX- posed to the air, necessitating constant use of fresh solutions and discarding of unused solution.

Inorder to prevent such deterioration of thickened plate moistening solutions, it has been attempted to inlic compound, or cyclic organic acids or their salts such as benzoates, salicylates, and the like. However, these materials to be effective must be present in a concentration of the order of onepercent or more in the solution, and when used in these concentrations, the preservative rapidly destroys the image on the plate. Accordingly, in practice, a fresh bath of fountain solution must be frequently used, and large amounts of solution must be discarded. This involves considerable inconvenience, waste and expense.

It has been found that aqueous plate dampening solu tions which contain highly dispersed silica instead of the products heretofore employed, are highly effective as fountain solutions in planographic printing. Thus, they maintain the desired balance between the'hydrophilie properties of the non-print background area and the inkreceptive water-repellent properties of the image over long. periods. The highly dispersed silica when used in such solutions is compatible with all of the other desired or usual ingredients, such as hygroscopic agents, buffering salts and other materials ordinarily employed in fountain solutions. In addition to these advantages, the highly dispersed silica is resistant to the deleterious effect of molds, bacteria and the like.

To immunize the suspensions of highly dispersed silica in water against spoilage by bacteria under ordinary conditions of use, minute amounts of a preservative are used in concentrations which have no effect upon the life of the image on the plate. Concentrations of about 0.1

percent or less of a preservative, such as formaldehyde or a phenolic compound, are-edective to prevent spoilage by bacteria.

The following are furth'er essential advantages arising out of the use of the fountain solutions accordant with the invention. The printing inks dry more quickly so that waiting periods, which are involved in particular between the'printing of two difierent colors in multicolor work, are reduced. The printing inks do not penetrate] V so deeply into the'pap'er; long runs are obtained because the silica solutions are not harmful. Use of the fountain solution accordant with the invention makes it unnecessary for the printing plates to be regummed during intervals when printing is suspended. This elimination of plate gumming results in a considerable improvement for offset printing, particularly in the case of multicolor printing, where hitherto it has been necessary for a number of printing plates to be regummed at each interruption of printing.

Highly dispersed silica suitable for the purpose of the invention is to be understood as silica (silicon dioxide) with an extremely fine average particle size of 5 to 40 millimicrons which is prepared commercially on a large scale by various processes, e.g. by hydrolizing silicon halides by means of water in the gas phase. Highly dispersed silica can be easily suspended in water without substantial sedimentation.

The present invention also includes a fountain solution for offset printing in which a highly dispersed mixed oxide consisting of aluminum oxide and silicon dioxide is present instead of the highly dispersed silica. Highl dispersed mixed oxides of this type are commercially available and are sold by the Degussa, Deutsche Goldund Silberscheideanstalt, Frankfurt am Main, for example They have also an average particle size of 5 to 40 millimicrons and are commercially available with a content of aluminum ranging from. about 1 to about 5 percent. The preferred mixed oxides substantially consist of silicon dioxide in the range from about 97% to 99.5% and aluminum oxide in the range from about 0.5 to about 3%.

For the preparation of the fountain solution accordant with the invention highly dispersed silica, e.g. the product marketed by the Degussa, Deutsche Goldund Silberscheideanstalt, Frankfurt am Main, under the registered trade mark Aerosil in the form of an uncompressed, very loose, amorphous bluish-white powder, may be suspended in water. The milky white silica supsensions with a content of l28% of silicon dioxide, likewise commercially available by the Degussa (under the designations K 314, K 315 or K 328) may also be used with advantage as starting material and diluted in water. Fountain solutions with very low concentrations of highly dispersed silica, e.g. lower than 0.04% of silicon dioxide, give remarkable results. In practice, solutions with about 0.04 to about 5% of silicon dioxide are advantageously used. Higher concentrations may, however, also be used without disadvantage. When using the mixed oxide increased concentrations are preferred, preferably about 0.4 to about 6%.

It can be advantageous for further additives to he included in the fountain solution accordant with the invention and these may include water-soluble or water-miscible additives whose use in fountain solutions is already known. Examples of further additives of this sort are ammonium phosphates, e.g. primary ammonium phosphate, citric acid salts, e.g. tertiary sodium citrate, polyvalent alcohols, such as glycerine, glycol, sorbite, polyglycols, dextrins, alginates carboxymethyl celluloses and vegetable gums; these may be added separately or several together to metal omde suspensions accordant with the invention. The preferred further additives are primary ammonium phosphate and glycerine, a mixture thereof, or tertiary sodium citrate.

Small amounts of the further additives are effective, the lower limit being not critical. At first, the effect rises with an increase in quantity. It is not favorable, however, to greatly exceed the amount of about 5 moles of further additives since no further increase of effect occurs. Preferably, not more than about 5 and not less than about 0.1 moles of additive to each mole of finely divided oxide are used.

The quantity to be added in each case depends on the additive in question and on the kind of metal oxide used. It cannot be stated beforehand but must be determined by a test which is not difiicult to perform. In general, it

can be said that when using liquid further additives, quantities approaching the upper limit of about 5 molcs of additive per 1 mole of metal oxide are preferred, while when using solid further additives quantities lying nearer the lower limit of about 0.1 mol of additive per mole of metal oxide are preferred.

Examples (1) A fountain solution very suitable for use in the planographic printing process is prepared from 975 cc. of water 25 cc. of an aqueous silica suspension containing 15% of finely divided silicon dioxide, e.g. the product available under the trade name K 315 Aerosil (registered trade mark of the Degussa Deutsche Goldund Silberscheideanstalt, Frankfurt am Main).

The pH value of the fountain solution is 56.- It is used without further treatment as a fountain solution.

An ofiset fountain solution that can be used with equally good results is obtained if approximately equivalent quantitles of a product containing 2% of aluminum oxide and 98% of silicon oxide, sold by the Degussa under the designation Aerosil AL 0111/200 is homogeneously distributed in the fountain solution instead of the above named K 315 suspension.

(2) A fountain solution for planographic printing is prepared from 500 cc. of water 250 cc. of a silica suspension containing 15% of finely divided silicon dioxide (cf. Example 1) 10 g. of primary ammonium phosphate 250 cc. of glycerine.

For use in the offset printing machine the concentrated preparation given above is diluted with water to ten times its volume. The pH value is then between 5.0 and 5.5. Formaldehyde or another disinfectant may be added to the diluted solution.

(3) An excellent fountain solution for offset printing is obtained if 5 g. of tertiary sodium citrate are added to the mixture described in Example 1 and homogeneously distributed therein.

Having thus described the invention, what is claimed 1. A fountain solution adapted for use in an offset printing process comprising an aqueous suspension of about 0.4 to about 6 percent of a mixture of finely divided silicon dioxide and finely divided aluminum oxide, the mixture containing about 97 to about 99.5 percent silicon dioxide and about 0.5 to about 3 percent of aluminum oxide and having an average particle size in the range of about 5 to about 40 millimicrons.

2. A fountain solution according to claim 1 including, in addition, a hygroscopic agent.

3. A fountain solution according to claim 1 in which the pH is below 7 and, in addition, a buffering agent is included. I

4. In a planographic printing process, the improvement which comprises dampening the printing plate with a fountain solution comprising an aqueous suspension of about 0.4 to about 6 percent of a mixture of finely divided silicon dioxide and finely divided aluminum oxide, the mixture containing about 97 to 99.5 percent silicon dioxide and about 0.5 to about 3 percent of aluminum oxide and having an average particle size in the range of about 5 to about 40 millimicrons.

5. A process according to claim 4 in which the fountain solution includes, in addition, a hygroscopic agent.

6. A process according to claim 4 in which the pH of the fountain solution is below 7 and, in addition, a buffering agent is included.

(References on following page) References Cited in the file of this patent 6 Nichols Feb. 5, 1957 Her May 6, 1958 OTHER REFERENCES UNITED STATES PATENTS 28331661 slmons 1938 Mellor: Comprehensive Treatise on Inorganic and Simons P 1939 5 Theoretical Chemistry, vol. 6, pub. 1925, by Longmans, Worthen Dec. 19, 1950 Green and Co., N.Y., only pp. 290 to 293, 470 and 471 Worthen et a1. June 22, 1954 made of record. (Copy available in Div. 59.) 

1. A FOUNTAIN SOLUTION ADAPTED FRO USE IN AN OFFSET PRINTING PROCESS COMPRISING AN AQUEOUS SUSPENSION OF ABOUT 0.4 TO ABOUT 6 PERCENT OF A MIXTURE OF FINELY DIVIDED SILICON DIOXIDE AND FINELY DIVIDED ALUMINUM OXIDE, THE MIXTURE CONTAINING ABOUT 97 TO ABOUT 99.5 PERCENT SILICON DIOXIDE AND ABOUT 0.5 TO ABOUT 3 PERCENT OF ALUMINUM OXIDE AND HAVING AN AVERAGE PARTICLE SIZE IN THE RANGE OF ABOUT 5 TO ABOUT 40 MILLIMICRONS. 